Police shot and killed "several dozen" people in northwestern Xinjiang province during clashes on the eve of an important Muslim holiday, Chinese authorities confirm.
Reporting of the incident was delayed almost 48 hours, and details remained vague.
The clashes took place Sunday night and Monday morning in villages near Yarkand, also known as Shache, a desert oasis near China's western border with Afghanistan and Tajikistan.
A report released by the official Xinhua news agency late Tuesday said several hundred people armed with knives and axes attacked local government and police offices in Ailixihu township, then launched a similar attack in adjacent Huangdi township.
"They smashed and burned multiple vehicles and slashed innocent civilians,'' the Xinhua report said. "Police responded swiftly and shot and killed several dozen assailants.''
Unconfirmed reports from people who were in the area said 13 police and 20 protesters were killed.
Chinese police in the region have taken up arms and adopted shoot-to-kill policies after a string of terror attacks.
Tourists who were in the area described military checkpoints on roads leading into and out of Yarkand. One tourist who asked not to be quoted by name said she saw a convoy of 20 canvas-covered military trucks driving into Yarkand on Tuesday night.
The tourist also said Internet and telephone service had been cut off intermittently.
A blogger wrote that the altercation started when police were "doing an inspection in a village."
"All police officers have been asked to cancel their vacations and return to their positions to be ready,'' wrote the blogger, who identified himself as PoliceX. He wrote that as many as 300 people were involved.
Yarkand includes a large community of Uighurs, a Muslim minority that speaks a Turkic language. Uighur fundamentalists are blamed for a deadly string of bombings and knifings around China that have left more than 150 dead over the past year.
The Communist Party has attempted to rein in Islamic religious activities, with such measures as banning teachers and students from fasting for Ramadan. This week is the three-day Eid festival that ends the holy month.